1. Field of the Invention
The present invention relates generally to the construction of catheters capable of being introduced into a patient's vascular system. In particular, the present invention relates to atherectomy devices which use an inflatable balloon for effecting contact between an interventional or diagnostic implement and the blood vessel wall.
Atherosclerosis is a condition characterized by fatty deposits (atheromas) in the intimal lining of a patient's blood vessels. Atherosclerosis can have many manifestations, including angina, hypertension, myocardial infarction, strokes, and the like. Initially, the atheromas deposited on the blood vessel walls remain relatively soft and tractable. Over time, however, the soft atheromic material becomes a calcified and hardened plaque. Regions of the blood vessel which are blocked by atheroma, plaque, or other material are generally referred to as stenoses, and the blocking material as stenotic material.
Atherectomy is a procedure which has been developed for removing stenotic material from the vascular system, usually before substantial calcification has occurred. Atherectomy procedures can utilize a variety of special catheters having severing instruments located at a distal end thereof and, often, an inflatable balloon for positioning the severing instrument. Usually, the catheter is located within the vascular system so that the severing instrument lies adjacent the stenotic region, and the balloon is inflated to bring the severing instrument into close proximity to the stenotic material. The severing instrument is then actuated to excise the released portion of the stenotic material, and the severed material captured to prevent the release of emboli.
The severing instrument on the atherectomy catheter can take a variety of forms, including fixed blades (requiring movement of the entire catheter to effect cutting) and movable blades which can be actuated within a stationary housing at the distal end of the catheter. Of particular interest to the present invention are atherectomy catheters of the type described in European Patent Application 163 502, owned by the assignee of the present invention. Such atherectomy catheters include a cutter housing attached to the distal end of a torqueable catheter body. A circular cutting blade is disposed within the housing and secured to the distal end of a rotatable drive shaft. An elongate aperture formed on one side of the housing allows the intrusion of stenotic material which may then be severed by rotating and axially translating the cutting blade. An inflatable balloon is disposed on the side of the housing opposite to the aperture so that the housing can be urged against the stenotic material on a blood vessel wall.
Although such atherectomy catheters have enjoyed substantial success and acceptance in the medical community, expansion of the positioning balloon required to laterally shift the cutter housing can have undesired effects on the adjacent blood vessel wall. For example, if the blood vessel wall in contact with the balloon is generally healthy, expansion of the balloon can cause damage. If, as is more likely, there are deposits of stenotic material on the blood vessel wall in contact with the positioning balloon, expansion of the balloon can compress the stenotic material in a manner similar to that of an angioplasty balloon. While such compression is not necessarily harmful, it renders subsequent excision of the stenotic material using the atherectomy catheter much more difficult.
A more serious shortcoming of previous atherectomy positioning balloons has been an inability to stably position the housing during the atherectomy procedure. For example, in tight stenotic regions, expansion of the positioning balloons can cause the cutter housing to be longitudinally displaced from its original position, rendering the desired cut problematic. Moreover, the stenotic material itself may be dislodged from its original position, which can interfere with positioning of the cutter housing and, in a worse instance, cause the release of stenotic material into the blood flow.
For these reasons, it would be desirable to provide improved positioning balloons for atherectomy devices and other catheters. It would be particularly desirable to provide positioning balloons which would allow for stable positioning of a cutter housing or other interventional device within a blood vessel within a wide variety of conditions. Moreover, it would be desirable if such position balloons were inherently less likely to damage or dilatate a blood vessel during performance of an interventional procedure.
2. Description of the Background Art and Related Applications
European Patent Application 163 502 is discussed above and corresponds to copending U.S. patent application Ser. No. 07/298,846, the disclosure of which is incorporated herein by reference. Similar atherectomy catheter designs which employ inflatable balloons for positioning a distal housing are described in U.S. Pat. Nos. 4,669,469; 4,771,774; and 4,781,186, and copending application Ser. Nos. 07/243,397; 07/045,916; and 07/117,072, the disclosures of which are incorporated herein by reference. Angioplasty and other vascular catheters employing spaced-apart balloons at their distal ends are described in U.S. Pat. Nos. 4,573,966; 4,610,662; 4,636,195; and 4,794,928.